Field of the Invention
The invention is based on a fuel metering unit for a high-pressure fuel pump.
Description of the Prior Art
One such fuel metering unit is known from German Patent Disclosure DE 10 2005 025 872 A1. This fuel metering unit serves to regulate the delivery quantity on the intake side of a high-pressure fuel pump that is part of a fuel injection system of an internal combustion engine. The fuel metering unit has a regulating valve which is actuated by an electromagnet and has a valve member and by which different flow cross sections can be established in the intake region of the high-pressure fuel pump, making it possible to regulate the delivery quantity of the high-pressure fuel pump. The electromagnet has an armature and a movable armature bolt, by which bolt the valve member is movable. The armature bolt is axially displaceably guided in at least one bearing bush. This at least one bearing bush may be made from bronze, for instance. Typically, bearing bushes are produced by rolling from a strip material, so that they have a cross joint. During operation of the fuel metering unit, swelling of the bearing bush can occur, causing it to widen. Moreover, the dimensional stability of such rolled bearing bushes may not be sufficient under some circumstances. It is also known for such bearing bushes to be provided, in the region of the bearing face in which the armature bolt is guided, with a coating, for instance of PTFE, in order to improve the sliding properties and keep wear low. However, the production of such coatings will no longer be permitted in various markets, such as the United States, because of their environmental harmfulness (for instance, using PFOA). The usual rolled bearing bushes have a slight wall thickness, so that a receptacle corresponding in diameter to approximately the diameter of the armature bolt is necessary for the bearing bush.